Giant Robber Fly - Promachus sp.
Order Diptera / Suborder Brachycera / Infraorder Muscomorpha / Family Asilidae -- robber flies
Live adult female robber flies photographed in the wild at Winfield, Illinois, USA.
Taxon & gender verified by Fritz Geller-Grimm
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  Robber Fly - Promachus sp.

I watched as this huge robber fly pounced on a honey bee that was busy gathering nectar. The next 10 minutes was spent following her around as she flew from perch to perch trying to eat her meal in peace. Finally, the unfortunate bee carcass was dropped, and off she flew.

Robber flies of this size (probably 30-35mm) do not fly so fast you cannot follow them - plus they have a low buzzing-rustling sound that greatly aids in pursuit. This is a truly awesome insect, and I relish each encounter I have with them.

These photographs were taken back in 2002 with a Kodak DC4800 point-and-shoot camera (3.2Mb) with add-on magnifying lens, using available light. Post camera treatment with Canon Photo Professional - sharpness and color saturation increased slightly; cropped, and that's it.

This camera was my mainstay for 3 years. Kodak sold an adapter kit with three magnifying lenses; the adapter fit over the lens barrel and the lenses screwed into the adapter. What I really liked about the camera was it had an external flash adapter. I originally used a Vivitar flash from my old Nikon FM camera accessories from the 1970s. It had a "Varipower" plug-in to manually vary the flash intensity. All the flash pictures I took with that camera were dialed in with no flash metering at all.

Kodak DC4800 Zoom Camera

Robber Fly
Female Robber Fly with Honey Bee Prey

There are over 7,000 species of robber flies world wide; nearly 1,000 in North America. 

All robber flies have stout, spiny legs, a dense moustache of bristles on the face (mystax), and 3 simple eyes (ocelli) in a characteristic depression between their two large compound eyes. The mystax helps protect the head and face when the fly encounters prey bent on defense. The antennae are short, 3-segmented, sometimes with a bristle-like structure called an arista.

The short, strong proboscis is used to stab and inject victims with saliva containing neurotoxic and proteolytic enzymes which paralyze and digest the insides; the fly then sucks the liquefied meal much like we vacuum up an ice cream soda through a straw. Many species have long, tapering abdomens, sometimes with a sword-like ovipositor. Others are fat-bodied bumble bee mimics; the effect is quite convincing.

 

Robber Fly
Photo shows the diagnostic depression between the large compound eyes. She is sucking the liquified juices from the captured honeybee.

 

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